Railway track circuit apparatus



Nov. 22, 1966 c. E. STAPLES 3,287,554

RAILWAY TRACK CIRCUIT APPARATUS Filed Nov. 1, 1963 2 Sheets-Sheet 2 T'mze amin Locad 1 INVENTOR.

HIS AZTTORZVEY' United States Patent r 3,287,554 RAILWAY TRACK CIRCUIT APPARATUS Crawford E. Staples, Edgewood, Pa., assignor to Westinghouse Air Brake Company, Swissvale, Pa., a corporation of Pennsylvania Filed Nov. 1, 1963, Ser. No. 320,864 12 Claims. (Cl. 246-35) This invention relates to railway track circuit apparatus, and more particularly to a single rail track circuit for direct current propulsion territory in which the direct current propulsion power is obtained from mercury arc rectifiers or similar static rectification sources. t

In direct current railway propulsion systems a thir rail or an overhead line is often employed as one conductor for the propulsion power, and one of the track rails is electric-ally continuous to serve as a return conductor. The other track rail is" frequently dividedinto insulated block sections for signaling and control purposes, and control is effected by connecting a source of 'A.C. signaling current across the rails at one end of each section and an alternating current responsive track relay across the other'end of each section. -In such systems when the direct current power for propulsion is'obtained from mercury arc rectifiers or similar static rectification devices, signaling problems have been encountered where the signal source is alternating current of the same frequency as the propulsion sourcebefore it is'rectified. In most instances, due to economic considerations and other factors, a single alternating current source, such as 60 cycles per second, is available forthe alternating current signal source, and, when rectified, for the direct current propulsion power. Thus with 'one rectifier anode misfiring, a 60 cycle ripple voltage appears in the propulsion power and is of the same frequency as the alternating current power source. This ripple voltage is approximately 6% of the direct current propulsion voltage. With track circuits fed from this same power source the ripple voltage will vary in phase with respect to the track circuit voltage depending on which rectifier unit misfires.

. Other factors may also shift these phase relations, such as the direction of propulsion current drawn by moving trains. Generally, the relay employed in such a track circuit is the type known. as an A.C. two-element vane type relay having a control or track winding electrically connected to one end of the block section, and a local winding connected to a local source of alternating current which is generally of the same frequency as the signaling current. Each winding is wound about its own respective core member and a non-ferrous vane is interposed between the two core members for pivotal movement therebetween. The relay contacts are actuated by the movement of the vane which is determined by the torque produced by induction currents within the vane caused by the fluxes from the respective core members being in quadrature. Consequently, this type of relay is phase sensitive inasmuch as operation thereof is dependent upon the phase displacement between thecurrent in the local winding and the current in the control or track winding, which displacement is usually in the order of 90 degrees. However, while 90-degree displacement is desired, the track relay can still operate if the current in the control or track winding has a component of sufficient magnitude in quadrature with the local winding current.

By way of example, if the propulsion direct current is obtained by means of mercury arc rectifiers, there will be a ripple of power'frequency multiplied by the number of rectifier anodes. Thus with a 60 cycle three-phase supply and twelve rectifier anodes there is a 720 cycle ripple. This ripple does not affect the track circuit. Should one of the anodes of a rectifier fail to fire there is a power Patented Nov. 22, 1966 frequency ripple present which will tend to operate the relay. With this particular type of relay the phase displacement with respect to the local winding of the relay must be considered. With twelve-phase rectification, failure of one particular anode will give a ripple with a phase displacement that is not more than 15 degrees from the displacement that will give maximum torque for a given voltage. This ripple voltage is approximately 6% of the direct current voltage. Therefore, under certain conditions of rectifier anode failure, witha train occupying the block section, the ripple voltage, if it is large enough and the phase angles are in the proper relation, will cause pickup or drop-away of the relay to give a false indication of the occupancy and nonoccupancy of a particular block section and thus create hazardous situations. Furthermore, with the higher currents in the propulsion rail as a result of high acceleration railways cars and the increased number of cars to be pulled by a single engine, or an increased number of multiple unit self-propelled cars, propulsion current surges are often encountered of sufficient magnitude to cause a momentary movement of the vane, and thereby actuate the relay falsely. I

In prior art practices the relay has been connected across the other end of the block section directly or with an isolating transformer interposed therebetween to eliminate direct current in the control winding of the track relay. However, such schemes still permit the ripple voltage and the propulsion current surges to actuate the relay and therefore are unsatisfactory as a solution to V the problem.

' Accordingly, it is an object of my invention to provide a new and improved alternating current signaling system in single rail track circuits for direct current propulsion.

It is another object of my invention to provide a new and improved alternating current track circuit which immunizes the track relay toadverse effects of ripple from the direct current propulsion current.

It is a further object of my invention to provide a new and improved alternating current track circuit wherein the track relay is protected from adverse operation due to direct current propulsion surges.

l ing train and the point of connection of the matching transformer to the propulsion rail. This voltage drop causes current to flow through the primary of the matching transformer, its series resistance, the insulated signaling rail, and through the truck to the propulsion rail. Upon a predetermined amount of current flowing in this circuit the matching transformer will saturate to prevent the transfer to the secondary of the matching transformer of any undesirable ripple which may be present, and likewise prevent the transfer of high direct current propulsion surges. The current limiting resistor results in a voltage drop thereacross to limit the voltage impressed upon the primary of the matching transformer to thereby permit utilization of a more economical transv former which will saturate at a lower value of direct Further objects, features and advantages of the present invention will become readily apparent as the following detailed description of the invention unfolds and when taken in conjunction with the drawings wherein:

FIG. 1 schematically illustrates one embodiment of my invention;

FIG. 2 graphically illustrates the impedance characteristics of the matching transformer employed in my invention;

FIG. 3 is a diagrammatic view of an alternating current two-element vane type track relay;

FIG. 4 graphically illustrates the effect of direct current propulsion surges;

FIG. 5 is a schematic of a modification according to my invention; and

FIG. 6 schematically illustrates an impedance bond in a two-rail track circuit.

Referring now to FIG. 1, there is shown a circuit comprising an alternating current power source 10 which is multiple-phase. The power from the alternating current source 10 is rectified through rectifier 12, the output of which is connected across an overhead line or a third rail 14 and an electrically continuous track propulsion rail 16. The rectifier 12 is a multiple-phase mercury arc rectifier or a similar multiple-phase static rectifier. The propulsion rail 16 serves as a negative return conductor for the direct current propulsion power. The other line of rails is divided into insulated signaling rail sections 18 which are insulated by suitable insulating means 19 at either end thereof to form a block section. For signaling and control purposes there is shown a circuit consisting of a feed or track transformer 20 whose primary 22 is connected to a suitable alternating current signal source (not shown), which is generally a single phase branch from the multiple hase alternating current source 10. The secondary 24 of the track transformer 20 is in series with a current limiting resistor 26, an insulated signaling rail section 18, a current limiting resistor 30, the primary 34 of a saturable matching transformer 28, and a portion of the electrically continuous propulsion rail 16. The secondary 32 of the matching transformer 28 is connected to the track winding 40 of a two-winding vane type alternating current responsive track relay 36 (partially shown in FIG. 3). With the track circuit unoccupied current flows from the secondary winding 24 of the track transformer 20 through both track rails 16 and 18 of the block section and the resistors 26 and 30 to the primary winding 34 of transformer 28. The secondary winding 32 of transformer 28 is thereby energized and energizes the track winding 40 of relay 36 to actuate the contact 37 to one of contact points 37a and 37b to control a track signal, for example. The track relay 36 has a local winding 38 (see FIG. 3) which is continually energized from a local source of alternating current of the same frequency as the alternating current power source 10, and the alternating current signal source. As will be discussed later, the phase angle of the current for the local winding 38 with respect to the current for the track winding 40 must be approximately 90 degrees for proper operation of the track relay 36, and both windings must be energized concurrently.

With the block section occupied, the track transformer 20 and the rails are shunted by the truck 42 (shown in dotted lines) of the train and the alternating current signaling source is rendered ineffective to operate the track relay 36. The resistor 26 in series with the secondary 24 of the track transformer 20 limits the current flowing through the secondary 24 of the track transformer 20 through the truck 42 land through the resistor 26. With the rails shunted, the track winding 40 of the track relay 36 is deenergized to deactuate the relay contact 37. However, due to the direct current flowing through the propulsion rail 16, a direct current voltage drop exists between the truck 42 and point B where the primary 34 of the matching transformer 28 is connected to the propulsion rail 16. Thus it can be seen that a direct current passes from truck 42 to point B through the insulated signaling rai-l section 18, through the resistor 30, and through the primary 34 of the matching transformer 28, where it is limited by the value of the current limiting resistor 30.

A diagrammatic illustration of the alternating current responsive track relay 36 is shown in FIG. 3 and is the type known as a two-element vane type relay having a local winding 38 connected to a local source of alternating current power of the same frequency as the signaling current, and a track Winding 40 connected to the secondary 32 of the matching transformer 28. A non-ferrous vane 44 is pivoted about an axis 46 and is positioned in inductive relationship between an E core 48 and a C core 50. Wound about the center leg of the E core 48 is the local winding 38, and wound about the C core 50 is the track winding 40. Each winding when energized induces eddy currents in the non-ferrous vane 44, and when the proper phase angle betweenthe fluxes from the respective core members is present, a torque is produced to induc-' tively move the vane 44 about its pivot axis 46. The relay contacts (not shown) are mechanically actuated by this movement, and since it is well known in the art and does not form a part of the present invention it is not shown. Relays of this type are well known in the art and are described in Chapter X of American Railway Signaling Principles and Practices under the heading Alternating Current Relays.

The optimum phase displacement to produce maximum torque in this type of relay is 90 degrees; however, sufficient torque to actuate the relay can still be produced if the phase angle is :15 degrees from optimum. Consequently, with the local winding energized, the relay could be actuated by ripple in the propulsion current depending on the freqeuncy, phase and magnitude of the ripple present. Similarly, high direct current propulsion surges may momentarily actuate the relay contacts.

By way of example, the propulsion power could be obtained from a 60 cycle, three-phase supply with twelve mercury arc rectifier anodes, which would produce a 720 cycle ripple. The total traction current is substantially steady state direct current and therefore does not affect the track circuit. Should one of the anodes of a rectifier fail to fire there is a 60 cycle power frequency ripple present which would tend to operate the relay. However, this would be dependent upon the phase relationship of the ripple with respect to the local winding. With twelvephase rectification, failure of one particular anode will give a ripple with a phase displacement that is not more than 15 degrees from the displacement that will give maximum torque for a given voltage. Thus if the ripple produced is of the same frequency as the signaling current frequency and is of the proper phase, it may cause sustained improper operation of the track relay 36 to thereby produce false signals which would be dangerous.

With the track circuit occupied at the track transformer end and a train accelerating toward the track relay end of the block section, power propulsion current surges may be encountered and the resistor 30 in series with the primary 34 of the matching transformer 28 will limit the amount of direct current flowing through the primary winding. Furthermore, as will be discussed hereinafter, the saturating characteristics of the matching transformer 28 prevent spurious operation of the track relay 36 under such conditions. As can be seen in the curve 29 of FIG. 2, the matching transformer 28 saturates as the amount of direct current in itsprimary 34 increases, and consequently the relay impedance reflected to the primary 34 of the matching transformer 28 decreases with increasing amounts of direct current in the primary 34.

The matching transformer 28 has direct current flowing meeting point of the secondary 24 of the track transformer 20 to the propulsion rail 16) and point B (the connecting point of the primary 34 of the matching transformer 28 to the propulsion rail 16). In operation the matching transformer 28 saturates at a value in excess of this amount of direct current in its primary 34 so that during nonoccupancy, the track relay 36 will respond to alternating current signals from the track transformer 20, but when the block section is occupied and the track rails are shunted, the matching transformer 28 saturates to prevent transmission of undesirable electrical fluctuations, such as ripple or surges, which may tend to operate the track relay 36.

In the specific relay characteristic shown the track relay 36 shows an input impedance of 2.23 ohms for the 60 cycle matching transformer 28 with the relay load and no direct current. For the relay 36 to pick up (just close front contacts) requires 0.715 volt, 0.32 ampere into the primary 34. The drop through the 5 ohm resistor 30 is 1.6 volts requiring a voltage of 2.05 volts at the rails for pickup at ideal phase relations. With, 6 ampere direct current through the primary 34, the primary impedance is 1.86 ohms and the input for pickup of the track relay 36 is 0.717 volt, 0.386 ampere, the increase in current being due to increased magnetizing current. The alternating current drop through the 5 ohm resistor 30 is now 1.93 volts and the rail voltage required for pickup is 2.35 volts. The margin against pickup from ripple is now 2.35/ 2.05 or 1.15 greater than with a nonsaturable transformer. This improved ripple protection is obtained from the regulation between the primary 34 and the track by the. i5 ohm resistor 30 resulting from change in magnetizing current.

Where the direct current surges are greater than anticipated, the ripple, if present, will increase in direct proportion. At the same time the magnetizing current will increase and regulation from resistor 30 will give increased protection. For example, the primary input impedance with 8 ampere direct current (2.4 volts ripple) will drop to 1.35 ohms, and the input for pickup will be 0.74 volt, 0.546 ampere. Rail voltage will be 3.12 volts. Pickup margin against ripple is 3.12/2.05 or 1.52 greater than for a nonsaturable transformer.

From the above examples it is evident that as the current involved in the ripple voltage increases the margin of safety also increases. Accordingly, the more current that flows in any one surge produces greater and greater protection against relay pickup from ripple.

The saturable transformer 28 therefore in combination with its series resistor 30 in the track connection affords protection from signal frequency ripple appearing in the direct current propulsion above that obtained with a nonsaturable transformer or the use of a multiple reactor. 7

FIG. 4 graphically illustrates. the effect of the saturable transformer 28 under direct current propulsion surges. Curve 52 shows the generally sinusoidal wave shape of the current in the local winding 38, while curve 54 (in dotted lines) shows how the direct current in the propulsion rail surges upon acceleration of a railway car. It can 'be seen that such a surge approximates one-half a cycle of a sine wave and is of such duration to create a phase differential which will cause the vane 44 of the track relay 36 to move and momentarily open the contacts of the relay, by transmission of the direct current pulse through a non-saturable type transformer. By utilizing the saturable type matching transformer 28 the decay time of the pulse 56 is increased to approximate that of the curve 54, whereby transmission of the pulse 56 through the saturable transformer 28 will be miniunized so that the effect of .such a direct current propulsion surge will be negligible to the track relay 36. Thus it can be seen that with either high direct current surges in the track circuit caused by accelerating. cars, or ripple in the track circuit caused by one or more anodes of the rectifier misfiring, the matching transformer 28 saturates to prevent transmission of these condition-s to the secondary 32 matching transformer 28 and thereby prevent energization of the track winding 40 of the track relay 36, and effectively immunize the track relay 36 from adverse eifects of ripple or high direct current propulsion surges.

Furthermore, it can be seen the use of the relay matching transformer 28 entirely eliminates steady state direct current in the control winding 40 of the track relay 36, thus eliminating noise and vibration of the vane 44 with the consequent contact wear and increase in resistance. Furthermore, the combination of transformer impedance characteristics and series resistor 30 eliminates false pickup of the track relay 36 due to effects of ripple on the direct current propulsion current. Additionally, the use of the matching transformer 28 permits centralized housing of the track relay 36 since line wire resistance is not an appreciable factor when a step-up transformer is used in combination with a high impedance track relay.

As shown in FIG. 5, a capacitor 58 can be inserted between the secondary 24 of the track transformer 20 and the track circuit, and thus no direct current propulsion current will flow in the track relay 36 of either of the transformer windings with the circuit unoccupied. Furthermore, with the track circuit occupied no direct current will fiow through the track transformer 20.

While the foregoing describes the invention in combination with a single rail track circuit, it is to be understood that it is within the contemplated scope of the invention to include double rail track circuits when the propulsion current flows through both rails and adjacent track sections are electrically joined by impedance bonds. In such circuits, poor rail bonding can cause an unbalance resulting in a similar direct current rail drop due to the difference in the rail resistance of the two rails. The signaling circuit would be identical to that shown and similar advantages would be obtained.

FIG. 6 shows the junction of a double rail track circuit wherein insulation 66 separates the rail into block sections on either side thereof. Suitable inductances 60 and 62 are connected across the track rails on either side of the insulated joints and the inductance are connected at the centers thereof by the conductor 64. Such impedance bonds are well known in the art and can be of the type described and illustrated in Letters Patent of the United States No. 1,286,401, issued December 3, 1918 to B. H. Peter, and assigned to the assignee of the present invention. It is obvious that the apparatus shown in FIG. 1 would be connected to the block section of double rail track circuits in the same manner.

Thus there has been shown and described a track circuit which effectively llIIlIl'lUI'llZBS the track relay 36 from adverse operation due to high direct current propulsion surges or ripple caused by the misfiring of a rectifier.

Obviously certain modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

Having thus described my invention, what I claim is:

1. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one of a pair of track rails and an additional conducting member adjacent to said' track rails, the other of said track rails 'being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a transformer having the primary thereof connected to the track rails at the other end of said block section;

() a track relay connected to the secondary of said transformer and being responsive to alternating current of said given frequency, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not 'be energized in response to direct current propulsion power surges or ripple from said rectification unit caused by the rnisfiring of one of said rectifiers.

2. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one of a pair of track rails and an additional conducting member adjacent to said track rails, the other of said track rails being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(c) current limiting means in series with the primary of said transformer;

(d) a track relay connected to the secondary of said transformer and being responsive to said alternating current signaling source, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that saidtrack relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to direct current propulsion power surges or ripple from said rectification unit caused by the misfiring of one of said rectifiers.

3. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one of a pair of track rails and an additional conducting member adjacent to said track rails, the other of said track rails being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) a track transformer having its secondary connected to the track rails at one end of said block section and the primary thereof connected to an alternating current signaling source of said given frequency;

(b) a matching transformer having the primary thereof connected to the track rails at the other end of said block section;

(c) a track relay connected to the secondary of said matching transformer and being responsive to said alternating current signaling source, said matching transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to direct current propulsion power surges or ripple from said rectification unit caused by the rnisfiring of one of said rectifiers.

4. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one of a pair of track rails and an additional conducting member adjacent to said track rails, the other of said track rails being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(c) a two-winding alternating current responsive inductive type track relay having one winding con nected to the secondary of said transformer, the other winding of said track relay being connected to a source of alternating current of said given frequency but displaced in phase from the current of said signaling source to supply part of the power to said track relay, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of non occupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to direct current propulsion power surges or ripple from said rectification unit caused by the misfiring of one of said rectifiers.

5. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one-of a pair of track rails and an additional conducting mem ber adjacent to said track rails, the other of said track rails being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) an alternating current signaling source of said given frequency being connected to the track rails at one end of said block section;

(b) direct current blocking means in series with said alternating current signaling source;

(c) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(d) a track relay connected to thesecondary of said transformer and being responsive to said alternating current signaling source, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will. not be energized in re-v sponse to direct current propulsion power surges or 9 ripple from said rectification un-it cause-d by the rnisfiring of one of said rectifiers.

6. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across an electrically continuous one of a pair of track rails and an additional conducting member adjacent to said track rails, the other of said track rails being divided into insulated sections, an insulated section of rail and a portion of the continuous rail forming a block section, said track circuit comprising:

(a) an alternating current signal-ing source of said given frequency connected to the track rails at one end of said block section;

(b) direct current blocking means in series with said alternating current signaling source;

(c) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(d) a two-winding alternating current responsive inductive type track relay connected to the secondary of said transformer, the other winding of said track relay being connected to the source of alternating current of said given frequency but displaced in phase from the current of said signaling source to supply part of the power to said track relay, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said 7 block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current frornsaid signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to direct current propulsion power surges or ripple from said rectification unit caused by the misfiring of one of said rectifiers.

7. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification uni-t being connected across the track rails of a block section, each block section being insulated from each adjacent block section for signaling purposes but being electrically connected by means for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(c) a track relay connected to the secondary of said transformer and being responsive to alternating current of said given frequency, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to spurious current fluctuations having a component of said given frequency when there is an unbalance in said circuit due to poor rail bonding or differing track rail resistances.

8. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across the track rails of a block section, each block section being insulated from each adjacent block section for signaling purposes but being electrically connected by impedance bonding for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a transformer having the primary thereof connected to the track rails at the other end of said block section;

(0) current limiting means in series with the primary of said transformer;

(d) a track relay connected to the secondary of said transformer and being responsive to alternating current of said given frequency, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling souce when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized. in response to spurious current fluctuations having a component of said given frequency when there is an unbalance in said circuit due-to poor rail bonding or differing track rail resistances.

' 9. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across the track rails of a block section, each block sect-ions being insulated from each adjacent block section for signaling purposes but being electrically connected by impedance bonding for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) a track transformer having its secondary connected to the track rails at one end of said block section and the primary thereof connected to an alternating current signaling source of said given frequency;

(b) a matching transformer having the primary thereof connected to the track rails at the other end of said block section;

(c) a track relay connected to the secondary of said transformer and being responsive to alternating current of said given frequency, said transformer being saturable at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to spurious current fluctuations having a component of said given frequency when there is an unbalance in said circuit due to poor rail bonding or differing track rail resistances.

10. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across the track rails of a block section, each block section being insulated from each adjacent block section for signaling purposes but being electrically connected by impedance bonding for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) a two-winding alternating current responsive inductive type track relay having a track winding and a local winding, said local Winding connected to a source of alternating current of said given frequency but displaced in phase from the current of said signaling source to supply part of the power to said track relay;

(c) and a saturable core transformer having its primary winding connected to the track rails at the other end of said block section, the secondary winding of said transformer connected to the track winding of said track relay, the parts being proportioned to saturate the core of said transformer at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to spurious current fluctuations having a component of said given frequency when there is an unbalance in said circuit due to poor rail bonding or differing track rail resistances.

11. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across the track rails of a block section, each block section being insulated from each adjacent block section for signaling purposes but being electrically connected by impedance bonding for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the trackrails at one end of said block section;

(b) direct current blocking means in series with said alternating current signaling source;

(c) a track relay responsive to said alternating current signaling source;

(d) and a saturable core transformer having its primary connected to the track rails at the other end of said block section, the secondary winding of said transformer connected to said track relay, the parts being proportioned to saturate the core of said transformer at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to spurious cur-rent fluctuations having a component of said given frequency when there is an unbalance in said circuit due to poor rail bonding or differing track rail resistances.

12. A track circuit for direct current propulsion territory where propulsion power is obtained from a static rectification unit with a plurality of rectifiers for rectifying alternating current of a given frequency, the output of said rectification unit being connected across the track rails of a block section, each block section being insulated from each adjacent block section for signaling purposes but being electrically connected by impedance bonding for continuously conducting the rectified propulsion current, said track circuit comprising:

(a) an alternating current signaling source of said given frequency connected to the track rails at one end of said block section;

(b) direct current blocking means in series with said alternating current signaling source;

(c) a two-winding alternating current responsive inductive type track relay having a track winding and a local winding, said local winding connected to a source of alternating current of said given frequency 'but displaced in phase from the current of said signaling source to supply part of the power to said track relay;

(d) and a saturable core transformer having its primary winding connected to the track rails at the other end of said block section, a current limiting resistor in series with said primary winding, the secondary winding of said transformer connected to the track winding of said track relay, the parts being proportioned to saturate the core of said transformer at a value of direct current in said block section in excess of that amount of direct current normally flowing in said block section during periods of nonoccupancy thereof such that said track relay will be energized in response to current from said signaling source when said block section is unoccupied but when the track rails are shunted by the wheels of a train said track relay will not be energized in response to spurious cur-rent fluctuations having a component of said given frequency when there is an unbalance in said circuit due to poor rail bonding or differing track rail resistances.

References Cited by the Examiner UNITED STATES PATENTS 1,599,470 9/1926 Hudd 246-34 FOREIGN PATENTS 826,553 1/1960 Great Britain.

ARTHUR L. LA POINT, Primary Examiner. S. B. GREEN, Assistant Examiner. 

1. A TRACK CIRCUIT FOR DIRECT CURRENT PROPULSION TERRITORY WHERE PROPULSION POWER IS OBTAINED FROM A STATIC RECTIFICATION UNIT WITH A PLURALITY OF RECTIFIERS FOR RECTIFYING ALTERNATING CURRENT OF A GIVEN FREQUENCY, THE OUTPUT OF SAID RECTIFICATION UNIT BEING CONNECTED ACROSS AN ELECTRICALLY CONTINUOUS ONE OF A PAIR OF TRACK RAILS AND AN ADDITIONAL CONDUCTING MEMBER ADJACENT TO SAID TRACK RAILS, THE OTHER OF SAID TRACK RAILS BEING DIVIDED INTO INSULATED SECTIONS, AN INSULATED SECTION OF RAIL AND A PORTION OF THE CONTINUOUS RAIL FORMING A BLOCK SECTION, SAID TRACK CIRCUIT COMPRISING: (A) AN ALTERNATING CURRENT SIGNALING SOURCE OF SAID GIVEN FREQUENCY CONNECTED TO THE TRACK RAILS AT ONE END OF SAID BLOCK SECTION; (B) A TRANSFORMER HAVING THE PRIMARY THEREOF CONNECTED TO THE TRACK RAILS AT THE OTHER END OF SAID BLOCK SECTION; (C) A TRACK RELAY CONNECTED TO THE SECONDARY OF SAID TRANSFORMER AND BEING RESPONSIVE TO ALTERNATING CURRENT OF SAID GIVEN FREQUENCY, SAID TRANSFORMER BEING SATURABLE AT A VALUE OF DIRECT CURRENT IN SAID BLOCK SECTION IN EXCESS OF THAT AMOUNT OF DIRECT CURRENT NORMALLY FLOWING IN SAID BLOCK SECTION DURING PERIODS OF NONOCCUPANCY THEREOF SUCH THAT SAID TRACK RELAY WILL BE ENERGIZED IN RESPONSE TO CURRENT FROM SAID SIGNALING SOURCE WHEN SAID BLOCK SECTION IS UNOCCUPIED BUT WHEN THE TRACK RAILS ARE SHUNTED BY THE WHEELS OF A TRAIN SAID TRACK RELAY WILL NOT BE ENERGIZED IN RESPONSE TO DIRECT CURRENT PROPULSION POWER SURGES OR RIPPLE FROM SAID RECTIFICATION UNIT CAUSED BY THE MISFIRING OF ONE OF SAID RECTIFIERS. 